When radio base stations are deployed, the performance in radio often needs to be monitored. In some countries e.g. Japan and Korea, there are mandatory requirements for regular measurements of radio performance of active radio base stations. During the measurement, traffic in the cell should not be switched off, whereby the radio base station shall remain in a normal transmitting state during the measurement.
Measurements on radio performance can be derived through either a fixed mounted RF (radio frequency) directional coupler, connected directly on each of the radio base station antenna connectors, or through an RF directional coupler housed inside the radio base station equipment and accessible through one extra connector per antenna connector.
New radio base stations are being developed, e.g. for 5G (fifth generation). These radio base stations operate at higher frequencies where beamforming is necessary in order to achieve sufficient coverage and performance. This implies that the number of transmitter and receiver chains are increased greatly compared to previous generations of radio base stations. Consequently, AAS (Active Antenna System) are commonly developed for such radio base stations. Previous generations of radio base stations normally have 2 or 4 transmitter and receiver chains at the most, while the AAS radio base station may have e.g. 32, 64, 128, 256 or even 512 transmitter and receiver chains depending on operating frequency and deployment. One of many parameters which make sense to be measured for AAS radio base stations, is total radiated power, encompassing the power for all transmitter chains.
Moreover, many AAS radio base station have the antennas integrated, whereby the use of externally fixed mounted external direction couplers for measuring power is not feasible.
For AAS with a higher number of antennas, adding connectors for each transmitter chain is not a feasible solution, since that would significantly impact size requirements and would increase complexity greatly. For mm-wave frequencies, due to high level of integration needed for technology, the problem is even more accentuated.